nsvt, max hr and exercise

I am a healthy 57 yo female, 5' 10", 150 lbs and all my life I have had periods when I had tachycardia, usually in the morning when I wake up--going upstairs etc. Several years ago I began having short, spontaneous--but infrequent--bouts of tachycardia that made me briefly dizzy but that hasn't happened in the past couple of years.  When I'm really fit it seems to mostly disappear.

I exercise strenuously at least 5 days a week--both bicycling and swimming, typically an hour at a time, although one bike ride a week might be 35 miles in 2+ hours. My heart rate during peak effort is typically over 100% of my predicted maximum HR.  I noticed recently that while my heart rate came down rapidly when I stopped exercising, it never went back to normal, but stayed about 20 bpm above normal.  When I ride at  the rate mentioned above, I can still carry on a conversation and am not uncomfortable.

During a recent holter monitor test, I took a bike ride and as usual my heart rate got up in the 170's at times, and while it was at that rate I had a short run of tachycardia that took it up to 180.  My doctor says I have SNVT--to which I cannot find any references.

Is it possible that I just don't conform to the formula for predicted maximum hr, and this is normal for me?

My doctor prescribed bystolic at a low dose.  It has slowed my heart rate by about 20 bpm but I feel fine. My question is, do I really need to take this medication?  What would happen if I didn't?


This discussion is related to NSVT questions.